The present invention relates to processing of titanium bearing ores and more specifically to an improved process for low cost and high speed extraction, production and refining of titanium and titanium alloys.
The present invention is a further improvement of Dr. Joseph""s prior patents, U.S. Pat. No. 5,503,655 issued Apr. 2, 1995 and U.S. Pat. No. 6,136,060 issued Oct. 24, 2000, the disclosures of which are incorporated herein by reference. The first patent describes a process in which a liquid slag containing titanium dioxide is reduced to a mixture of titanium dioxide and iron; the iron is then separated out to produce about 95% pure titanium dioxide. In subsequent processing, the partially pure titanium dioxide is melted and processed to remove any residual iron and other impurities to form titanium dioxide powder.
The second patent discloses a process for production of titanium and titanium alloys using a reductive process under vacuum. The reduction step is carried out by molten metallic sodium, whereas in the present disclosure, the reductant could be any of magnesium, sodium, hydrogen, lithium, potassium, rubidium, cesium, francium, beryllium, calcium, strontium, barium or radium.
Canadian Patent No. 549299 to Gross et al. discloses the production of titanium metal by decomposing titanium halides under controlled temperatures. U.S. Pat. No. 4,793,854 to Shimotori et al. produces titanium by electrolysis of molten titanium slat followed by purification under high vacuum conditions.
A large number of prior art references describe various aspects of refining metals and particularly refining titanium. Great Britain Patent No 809,444 , U.S. Pat. No. 3,546,348 to DeCorso and U.S. Pat. No. 3,764,297 to Coad et al. describe the use of electric arcs under vacuum to melt metals. U.S. Pat. No. 2,997,760 to Hanks et al. describes melting metals under vacuum to remove volatile impurities. U.S. Pat. No. 3,237,254 (Hanks et al.), U.S. Pat. No. 3,342,250 (Treppschuh et al.) and U.S. Pat. No. 3,343,828 (Hunt) describe melting metals under vacuum with electron beam guns. U.S. Pat. No. 3,494,804 to Hanks et al. also describes vacuum heating with an electron beam gun and discloses the idea of using a xe2x80x9cskullxe2x80x9d to prevent contamination of a melt by the walls of a crucible. U.S. Pat. No. 4,027,722 to Hunt and U.S. Pat. No. 4,488,902, also to Hunt, describe additional details of electron beam based processes U.S. Pat. No. 3,210,454 to Morley and U.S. Pat. No. 4,838,340 to Entrekin et al. disclose the use of plasma torches to maintain metals in a molten state.
Titanium, especially some of its alloys such as titanium-aluminum-vanadium (Ti-6Al-4V) are important because they are ideally suited for a wide variety of applications in the aerospace, aircraft, military, and automotive fields. Titanium and its alloys, including that mentioned, combine the attractive properties of high strength and light weight with resistance to corrosion and stability under high temperatures. For example, titanium is very strong but only about 60% as dense as iron and parts made of titanium will weigh only 60% as much as the same part made of steel. While titanium is relatively easy to fabricate, there are numerous impediments to its widespread use. As demonstrated by the above cited references, refining titanium is energy intensive and involves significant costs in handling due to the need for toxic chemicals for its refining. Furthermore, in refining titanium, there may also be a high cost involved in disposing of the toxic byproducts produced in the refinery process.
Thus, it is a primary object of this invention to provide an improved and cost effective process for the production of high purity titanium and its alloys from a starting ore containing titanium, preferably in an oxide form.
Another object of the present invention is the conversion of a titanium bearing ore such as rutile or ilmenite to an essentially pure titanium tetrachloride followed by reduction to titanium which is then followed by refining of the titanium to a pure state and optionally alloying the same.
These objects and features of the present invention will become more apparent from the following detailed description which provides detailed information regarding both the process and apparatus and which is for purposes of illustration and should not be construed as a limitation on the present invention.
The present invention is a process for refining titanium containing ore and more particularly a sequence which involves converting the titanium ore to titanium tetrachloride, the latter continuously reduced to titanium metal in a plasma reactor in the presence of a metallic reductant under inert gas at atmospheric pressures. The resulting titanium is continuously fed and further processed to a relatively high purity while molten and under inert gas at atmospheric pressures followed optionally by alloying with other metals such as aluminum and vanadium.
First, titanium tetrachloride is produced from the ore and many of the impurities such as iron chloride and vanadium are removed in this step resulting in an intermediate with less than four parts per billion.
Then the titanium tetrachloride is reduced with molten magnesium or sodium, or alternatively with lithium, potassium, rubidium, cesium, francium, beryllium, calcium, strontium, barium or radium under inert gas at atmospheric pressures in a plasma reactor preferably using a hydrogen plasma. Thereafter, the molten titanium is processed in the presence of inert gas under atmospheric pressures (approximately 760 Torr ) and elevated temperatures. During this processing alloying optionally may take place.
An appreciation of the other aims and objectives of the present invention and an understanding of it may be achieved by referring to the accompanying drawings and description of a preferred embodiment.